It is well known that various thermoplastic materials having high dielectric loss coefficients may be melted by the application of radio frequency (RF) electric fields which excite and dielectrically heat the thermoplastic materials. This principle has been successfully applied to sealing plastic tubing. For example, the principle has been used to seal flexible plastic tubing containing medical or biological fluids used with medical apparatus and in the collection of blood from blood donors.
U.S. Pat. No. 4,013,860, issued Mar. 22, 1977 to Hosterman et al. for a "Hand Held Electro-Mechanism Sealer" describes an example of a hand held tubing sealer. The Hosterman tubing sealer compresses a flexible plastic medical tube between two jaws. RF energy is applied to the jaws, creating an electrical field. The electrical field excites and dielectrically heats the plastic tube compressed between the jaws, partially melting the plastic material of the tubing. The partially melted material welds together to form a hermetic fluid-tight seal. The fluid-tight seal divides the tube into two segments and prevents fluid communication between the two segments. The segments are physically connected by a thick web of plastic.
The Hosterman sealer has been advantageously used to facilitate the collection, transfer, and processing of blood from blood donors, and has further been used with the collection of separated blood components using a medical apparatus such as the blood component separation equipment manufactured by a subsidiary of the assignee of the present invention.
It is recognized as desirable under some circumstances to seal a plastic medical tube and divide it into two non-communicating segments without physically separating the segments from each other. It is further recognized as desirable under other circumstances to seal the tube dividing it into two non-communicating segments and physically separate the segments from each other. Although tubing sealers such as the Hosterman tubing sealer have been successfully used to seal plastic medical tubing, they have not generally been adaptable to sealing the tubing in a manner that facilitates separating the segments from each other. In those circumstances where the tube is to be sealed and separated it is often necessary to manually tear the two segments of the tube from each other. The thick web of plastic left by the Hosterman device may be difficult to tear. Furthermore, it is possible to inadvertently tear a segment of the tube instead of the web, impairing the sterility of the fluid in the tube and potentially exposing the operator to contact with the fluid which may be infectious or otherwise hazardous.
Alternatively the two segments may be cut from each other using a knife or scissors. The use of the knife or scissors increases the time required. Furthermore, the knife or scissors must be used with great care to avoid cutting into the seal, thereby impairing the sterility of the fluid, and potentially exposing the operator to contact with the fluid. Furthermore, when a knife or scissors cuts into the seal the knife or scissors may become contaminated, making it hazardous to use the knife or scissors for any purpose until it is cleaned or sterilized.
Although tubing sealers such as the Hosterman tubing sealer are highly reliable and safe, occasionally a seal made in a tube will fail during a sealing operation, potentially exposing the operator to contact with the fluid in the tube.
It has been proposed to provide ridges or other protrusions on the jaws of a tubing sealer to emboss the thick web creating a thinner area. In practice it has been found that such embossing jaws do not reliably produce an easily tearable web between the segments of the tube.
A thermoplastic material welding device which incorporates an electrode covering material is illustrated in Great Britain patent specification 797,202 published Jun. 25, 1958 on an application by Rado entitled "Radio Frequency Heating Electrodes".
It is against this background that the significant improvements and advancements of the present invention in the field of sealing plastic tubing have evolved.